FJ, I have just had 2 internal scans a week apart due to bleeding. The first one showed a sac and that's all. The next one a week later showed a blob with a heartbeat and measured 6w 3d. So if SIL was 5 - 6 weeks at the first scan then it would be too early to see anything. 1 week to 10 days later makes a huge difference.

It will be interesting to see if she does have twins there - keep us posted!!